Consulta: subjectFacets:"Meridional overturning circulation"
Registros recuperados: 14
Data/hora: 03/06/2024 00:50:18

Response of North-Atlantic Ocean circulation to atmospheric weather regimes
Provedor de dados: 5
Autores: Barrier, Nicolas; Cassou, Christophe; Deshayes, Julie; Treguier, Anne-marie.
A new framework is proposed for investigating the atmospheric forcing of North-Atlantic ocean circulation. Instead of using classical modes of variability, such as the North-Atlantic Oscillation (NAO) or the East-Atlantic Pattern, we here use the weather regimes paradigm. Using this framework we avoid problems associated with the assumptions of orthogonality and symmetry that are particular to modal analysis and known to be unsuitable for the NAO.  Using ocean-only historical and sensitivity experiments, we investigate the impacts of the four winter weather regimes on horizontal and overturning circulations. Our results suggest that the Atlantic Ridge (AR), NAO− and NAO+ regimes induce a fast (monthly to interannual timescales) adjustment of the gyres via...
Tipo: Text
Palavras-chave: Circulation; Dynamics; Meridional overturning circulation; Atm; Ocean Structure; Phenomena; Gyres; North Atlantic Oscillation; Wind; Physical Meteorology and Climatology; Climate classification; Regimes; Models and modeling; Ocean models.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00161/27258/25467.pdf

Dissolved organic nitrogen production and export by meridional overturning in the eastern subpolar North Atlantic
Provedor de dados: 5
Autores: Fernández-castro, Bieito; Álvarez, Marta; Nieto-cid, Mar; Zunino, Patricia; Mercier, Herle; Álvarez-salgado, Xosé Antón.
Dissolved organic matter (DOM) is produced in the surface and exported towards the deep ocean, adding ∼2 PgC yr−1 to the global carbon export. Due to its central role in the Meridional Overturning Circulation (MOC), the eastern subpolar North Atlantic (eSPNA) contributes largely to this export. Here we quantify the transport and budget of dissolved organic nitrogen (DON) in the eSPNA, in a box delimited by the OVIDE 2002 section and the Greenland‐Iceland‐Scotland sills. The MOC exports &gt;15.9 TgN yr−1 of DON downwards and, contrary to the extended view that these are materials of subtropical origin, up to 33% of the vertical flux derives from a net local DON production of 7.1 ± 2.6 TgN yr−1. The low C:N molar ratio of DOM production (7.4 ± 4.1) and the...
Tipo: Text
Palavras-chave: Dissolved organic matter; Nitrogen cycle; Meridional overturning circulation; Subpolar North Atlantic; Metabolic balance.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00485/59622/62649.pdf

A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years
Provedor de dados: 5
Autores: Hines, Sophia K. V.; Southon, John R.; Adkins, Jess F.
The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial-interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow...
Tipo: Text
Palavras-chave: Southern Ocean; Radiocarbon; Glacial interglacial climate change; Meridional overturning circulation; Southern Ocean fronts; Intermediate water.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00497/60838/64466.pdf

Multidecadal variability of the overturning circulation in presence of eddy turbulence
Provedor de dados: 5
Autores: Huck, Thierry; Arzel, Olivier; Sevellec, Florian.
At low-resolution, idealized ocean circulation models forced by prescribed differential surface heat fluxes show spontaneous multidecadal variability depending critically on eddy diffusivity coefficients. The existence of this critical threshold in the range of observational estimates legitimates some doubt on the relevance of such intrinsic oscillations in the real ocean. Through a series of numerical simulations with increasing resolution up to eddy-resolving ones (10 km) and various diapycnal diffusivities, this multidecadal variability proves a generic ubiquitous feature, at least in model versions with a flat bottom. The mean circulation largely changes in the process of refining the horizontal grid (along with the associated implicit viscosity and...
Tipo: Text
Palavras-chave: Circulation/ Dynamics; Meridional overturning circulation; Rossby waves; Turbulence; Variability; Multidecadal variability.
Ano: 2015
URL: http://archimer.ifremer.fr/doc/00251/36243/34798.pdf

Geostrophic Closure of the Zonally Averaged Atlantic Meridional Overturning Circulation
Provedor de dados: 5
Autores: Sevellec, Florian; Huck, Thierry.
It is typically assumed that the meridional density gradient in the North Atlantic is well and positively correlated with the Atlantic meridional overturning circulation (AMOC). In numerical "water-hosing" experiments, for example, imposing an anomalous freshwater flux in the Northern Hemisphere leads to a slowdown of the AMOC. However, on planetary scale, the first-order dynamics are linked to the geostrophic balance, relating the north-south pressure gradient to the zonal circulation. In this study, these two approaches are reconciled. At steady state and under geostrophic dynamics, an analytical expression is derived to relate the zonal and meridional pressure gradient. This solution is only valid where the meridional density gradient length scale is...
Tipo: Text
Palavras-chave: Meridional overturning circulation; Thermohaline circulation; Atm/Ocean Structure/ Phenomena; Ocean circulation; Baroclinic flows; Geographic location/entity; Ekman pumping; Circulation/ Dynamics; Atlantic Ocean.
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00323/43456/42843.pdf

Agulhas Leakage Predominantly Responds to the Southern Hemisphere Westerlies
Provedor de dados: 5
Autores: Durgadoo, Jonathan V.; Loveday, Benjamin R.; Reason, Chris J. C.; Penven, Pierrick; Biastoch, Arne.
The Agulhas Current plays a crucial role in the thermohaline circulation through its leakage into the South Atlantic Ocean. Under both past and present climates, the trade winds and westerlies could have the ability to modulate the amount of Indian-Atlantic inflow. Compelling arguments have been put forward suggesting that trade winds alone have little impact on the magnitude of Agulhas leakage. Here, employing three ocean models for robust analysisa global coarse-resolution, a regional eddy-permitting, and a nested high-resolution eddy-resolving configurationand systematically altering the position and intensity of the westerly wind belt in a series of sensitivity experiments, it is shown that the westerlies, in particular their intensity, control the...
Tipo: Text
Palavras-chave: Boundary currents; Meridional overturning circulation; Wind stress; Mesoscale models; Numerical analysis; Modeling.
Ano: 2013
URL: http://archimer.ifremer.fr/doc/00161/27247/25452.pdf

An inverse model of the large scale circulation in the South Indian Ocean
Provedor de dados: 5
Autores: Sultan, Emmanuelle; Mercier, Herle; Pollard, R.t.
An overview of the large-scale circulation of the South Indian Ocean (SIO) (10 degrees S-70 degrees S/20 degrees E-120 degrees E) is proposed based on historical hydrographic data (1903-1996) synthesized with a finite-difference inverse model. The in situ density, potential temperature and salinity fields of selected hydrographic stations are projected on the basis of EOFs. Then the EOF coefficients (the projected values) are interpolated on the model grid (1 degrees in latitude, 2 degrees in longitude) using an objective analysis whose spatial correlation functions are fitted to the data set. The resulting fields are the input of the inverse model. This procedure filters out the small-scale features. Twelve modes are needed to keep the vertical structures...
Tipo: Text
Palavras-chave: Mean circulation; Meridional overturning circulation; Weddell Gyre; Antarctic Circumpolar Current; Inverse model; Southern Indian Ocean.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-2672.pdf

Atlantic Meridional Overturning Circulation: Observed Transport and Variability
Provedor de dados: 5
Autores: Frajka-williams, Eleanor; Ansorge, Isabelle J.; Baehr, Johanna; Bryden, Harry L.; Chidichimo, Maria Paz; Cunningham, Stuart A.; Danabasoglu, Gokhan; Dong, Shenfu; Donohue, Kathleen A.; Elipot, Shane; Heimbach, Patrick; Holliday, N. Penny; Hummels, Rebecca; Jackson, Laura C.; Karstensen, Johannes; Lankhorst, Matthias; Le Bras, Isabela A.; Lozier, M. Susan; Mcdonagh, Elaine L.; Meinen, Christopher S.; Mercier, Herle; Moat, Bengamin I.; Perez, Renellys C; Piecuch, Christopher G.; Rhein, Monika; Srokosz, Meric A.; Trenberth, Kevin E.; Bacon, Sheldon; Forget, Gael; Goni, Gustavo; Kieke, Dagmar; Koelling, Jannes; Lamont, Tarron; Mccarthy, Gerard D.; Mertens, Christian; Send, Uwe; Smeed, David A.; Speich, Sabrina; Van Den Berg, Marcel; Volkov, Denis; Wilson, Chris.
The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basin AMOC observational systems have been put in place to continuously monitor meridional volume transport variability, and in some cases, heat, freshwater and carbon transport. These observational programs have been used to diagnose the magnitude and origins of transport variability, and to investigate impacts of variability on essential climate variables such as sea surface temperature, ocean heat content and...
Tipo: Text
Palavras-chave: Meridional overturning circulation; Thermohaline circulation; Observing systems; Ocean heat transport; Carbon storage; Moorings; Circulation variability.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00503/61507/65342.pdf

Meridional Overturning Circulation Transport Variability at 34.5 degrees S During 2009-2017: Baroclinic and Barotropic Flows and the Dueling Influence of the Boundaries
Provedor de dados: 5
Autores: Meinen, Christopher S.; Speich, Sabrina; Piola, Alberto R.; Ansorge, Isabelle; Campos, Edmo; Kersale, Marion; Terre Terrillon, Thierry; Chidichimo, Maria Paz; Lamont, Tarron; Sato, Olga T.; Perez, Renellys C.; Valla, Daniel; Van Den Berg, Marcel; Le Henaff, Matthieu; Dong, Shenfu; Garzoli, Silvia L.
Six years of simultaneous moored observations near the western and eastern boundaries of the South Atlantic are combined with satellite winds to produce a daily time series of the basin-wide meridional overturning circulation (MOC) volume transport at 34.5 degrees S. The results demonstrate that barotropic and baroclinic signals at both boundaries cause significant transport variations, and as such must be concurrently observed. The data, spanning similar to 20 months during 2009-2010 and similar to 4 years during 2013-2017, reveal a highly energetic MOC record with a temporal standard deviation of 8.3 Sv, and strong variations at time scales ranging from a few days to years (peak-to-peak range = 54.6 Sv). Seasonal transport variations are found to have...
Tipo: Text
Palavras-chave: Meridional overturning circulation; South Atlantic; Overturning; Volume transport; Observations.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00445/55612/57253.pdf

The Mechanisms of the Atlantic Meridional Overturning Circulation Slowdown Induced by Arctic Sea Ice Decline
Provedor de dados: 5
Autores: Liu, Wei; Fedorov, Alexey; Sevellec, Florian.
We explore the mechanisms by which Arctic sea ice decline affects the Atlantic meridional overturning circulation (AMOC) in a suite of numerical experiments perturbing the Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next similar to 100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in...
Tipo: Text
Palavras-chave: Arctic; Meridional overturning circulation; Climate models.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00599/71107/69388.pdf

A Lagrangian Method to Isolate the Impacts of Mixed Layer Subduction on the Meridional Overturning Circulation in a Numerical Model
Provedor de dados: 5
Autores: Thomas, Matthew; Treguier, Anne-marie; Blanke, Bruno; Deshayes, Julie; Voldoire, Aurore.
Large differences in the Atlantic meridional overturning circulation (AMOC) exhibited between the available ocean models pose problems as to how they can be interpreted for climate policy. A novel Lagrangian methodology has been developed for use with ocean models that enables a decomposition of the AMOC according to its source waters of subduction from the mixed layer of different geographical regions. The method is described here and used to decompose the AMOC of the Centre National de Recherches Météorologiques (CNRM) ocean model, which is approximately 4.5 Sv (1 Sv = 106 m3 s−1) too weak at 26°N, compared to observations. Contributions from mixed layer subduction to the peak AMOC at 26°N in the model are dominated by the Labrador Sea, which contributes...
Tipo: Text
Palavras-chave: Circulation; Dynamics; Convection; Lagrangian circulation; Transport; Meridional overturning circulation; Atm; Ocean Structure; Phenomena; Oceanic mixed layer; Models and modeling; General circulation models.
Ano: 2015
URL: http://archimer.ifremer.fr/doc/00284/39523/38016.pdf

Temporal variability of the meridional overturning circulation at 34.5°S: Results from two pilot boundary arrays in the South Atlantic
Provedor de dados: 5
Autores: Meinen, Christopher S.; Speich, Sabrina; Perez, Renellys C.; Dong, Shenfu; Piola, Alberto R.; Garzoli, Silvia L.; Gladyshev, Sergey; Baringer, Molly; Campos, Edmo J. D.
Data from two boundary arrays deployed along 34.5°S are combined to produce the first continuous in situ time series observations of the basin-wide meridional overturning circulation (MOC) in the South Atlantic. Daily estimates of the MOC between March 2009 and December 2010 range between 3 Sv and 39 Sv (1 Sv = 106 m3 s−1) after a 10 day low-pass filter is applied. Much of the variability in this ∼20 month record occurs at periods shorter than 100 days. Approximately two-thirds of the MOC variability is due to changes in the geostrophic (baroclinic plus barotropic) volume transport, with the remainder associated with the direct wind-forced Ekman transport. When low-pass filtered to match previously published analyses in the North Atlantic, the observed...
Tipo: Text
Palavras-chave: Meridional overturning circulation; Transport; South Atlantic; Inverted echo sounder; Bottom pressure.
Ano: 2013
URL: http://archimer.ifremer.fr/doc/00167/27789/25982.pdf

Can We Infer Diapycnal Mixing Rates from the World Ocean Temperature-Salinity Distribution?
Provedor de dados: 5
Autores: Arzel, Olivier; Colin De Verdiere, Alain.
The turbulent diapycnal mixing in the ocean is currently obtained from microstructure and finestructure measurements, dye experiments, and inverse models. This study presents a new method that infers the diapycnal mixing from low-resolution numerical calculations of the World Ocean whose temperatures and salinities are restored to the climatology. At the difference of robust general circulation ocean models, diapycnal diffusion is not prescribed but inferred. At steady state the buoyancy equation shows an equilibrium between the large-scale diapycnal advection and the restoring terms that take the place of the divergence of eddy buoyancy fluxes. The geography of the diapycnal flow reveals a strong regional variability of water mass transformations....
Tipo: Text
Palavras-chave: Diapycnal mixing; Eddies; Meridional overturning circulation; Mixing; Ocean circulation; General circulation models.
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00600/71197/69563.pdf

The Internal Generation of the Atlantic Ocean Interdecadal Variability
Provedor de dados: 5
Autores: Arzel, Olivier; Huck, Thierry; Colin De Verdiere, Alain.
Numerical simulations of a realistic ocean general circulation model forced by prescribed surface fluxes are used to study the origin and structure of intrinsic interdecadal variability of the ocean circulation. When eddy-induced turbulent diffusivities are low enough, spontaneous oscillations of the Atlantic meridional overturning circulation (AMOC) with periods O(20) yr and amplitude O(1) Sv (1 Sv ≡ 106 m3 s−1) emerge. The transition from the steady to the oscillatory regime is shown to be consistent with a supercritical Hopf bifurcation of the horizontal Peclet number. Adding atmospheric thermal damping is shown to have a very limited influence on the domain of existence of intrinsic variability. The spatial structure of the mode consists of a dipole of...
Tipo: Text
Palavras-chave: Instability; Meridional overturning circulation; Ocean circulation; Planetary waves; Climate variability; Multidecadal variability.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00464/57522/59708.pdf